During air conditioner (a/c) operation in a heating, ventilating and air conditioning (HVAC) system in a vehicle, moisture condenses out of the air that is being conditioned. The air is cooled by an evaporator and moisture physically condenses on the evaporator core. Because of the core design, this moisture often accumulates on the core fins. Because the evaporator core must be an efficient heat exchanger, it is designed with louvered or cupped fins. While these fins are efficient for forced air convection, they naturally do an excellent job of retaining moisture during and after normal air conditioner operation. When the vehicle is inoperative or the HVAC is turned off, air surrounds the moisture laden evaporator core within a plenum, chamber or ducting system which provides an environment for bacteria and other odor causing organisms.
During a/c operation, automatic HVAC systems will typically operate in a recirculation or partial recirculation mode under extreme operating conditions until the cabin approaches a comfortable level. At this point the system operates in outside air mode, unless manually overridden. Moisture in the air tends to condense on the evaporator core with more humid air causing more moisture to condense. That is to say, more moisture is condensed from the typically more humid outside air than from the less humid recirculated cabin air. At high levels of humidity, the a/c system compressor consumes more horsepower than at low levels of humidity. It is desirable to reduce overall a/c system energy consumption for greater fuel economy. While continuously operating in the recirculation or partial recirculation or partial recirculation or partial recirculation mode would greatly reduce compressor energy consumption, it would yield cabin air that is too dry and too cold for comfort. Accordingly, it will be appreciated that it would be highly desirable to have a system which factors in humidity conditions when choosing an operating mode and which reduces moisture condensed by the evaporator core to discourage microbial growth and odor.